ASTM D7895 - D 7895M - 19 (2025) 粉末涂覆绝缘系统用涂层粉末热耐久性的标准试验方法

VIP专免

那山那人那狗 2026-09-03 7 782.12KB 6 页 22星币

Designation: D7895/D7895M −19 (Reapproved 2025)
Standard Test Method for
Thermal Endurance of Coating Powders Used for Powder
Coating Insulation Systems
1
This standard is issued under the ﬁxed designation D7895/D7895M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method provides a procedure for evaluating
thermal endurance of coating powders by determining the
length of aging time at selected elevated temperatures required
to achieve dielectric breakdown at room temperature at a
pre-determined proof voltage. Thermal endurance is expressed
in terms of a temperature index.
1.2 This test method is applicable to insulating powders
used over a substrate material of steel.
1.3 Units—The values stated in either SI units or inch-
pound units are to be regarded separately as standard. The
values stated in each system are not necessarily exact equiva-
lents; therefore, each system shall be used independently of the
other. Combining values from the two systems is likely to
result in non-conformance with the standard.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
Speciﬁc precautionary statements are given in Section 7.
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
D149 Test Method for Dielectric Breakdown Voltage and
Dielectric Strength of Solid Electrical Insulating Materials
at Commercial Power Frequencies
D1711 Terminology Relating to Electrical Insulation
D5423 Speciﬁcation for Forced-Convection Laboratory Ov-
ens for Evaluation of Electrical Insulation
2.2 IEEE Document
3
IEEE 101A Simpliﬁed Method for Calculation of the Re-
gression Line
3. Terminology
3.1 Deﬁnitions:
3.1.1 For deﬁnitions of terms used in this test method refer
to Terminology D1711.
3.2 Deﬁnitions of Terms Speciﬁc to This Standard:
3.2.1 thermal endurance, n—an expression for the stability
of an electrical insulating material, or a simple combination of
materials, when maintained at elevated temperatures for ex-
tended periods of time.
3.3 Deﬁnitions—For deﬁnitions of terms used in this test
method refer to Terminology D1711.
4. Summary of Test Method
4.1 Specimens are aged in air at a minimum of three
temperatures above the expected use temperature of the mate-
rial. Exposure to ambient stress conditions, followed by
dielectric proof voltage tests in an electrically conductive
solution, are periodically conducted to determine the time of
aging at each elevated temperature required to reduce the
breakdown voltage to a preselected percentage of the original
breakdown value. These thermal life values are used to
construct a thermal endurance graph by means of which it is
possible to estimate a temperature index, corresponding to a
thermal life as speciﬁed in the material speciﬁcation or as
agreed upon between the user and the supplier. It is possible
that a material will have multiple indices, each corresponding
to a different thermal life as required by a given application.
5. Signiﬁcance and Use
5.1 A major factor affecting the life of insulating materials is
thermal degradation. It is possible that other factors, such as
1
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.01 on Electrical Insulating Products.
Current edition approved Dec. 1, 2025. Published December 2025. Originally
approved in 2014. Last previous edition approved in 2019 as D7895/D7895M – 19.
DOI: 10.1520/D7895_D7895M-19R25.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at www.astm.org/contact. For Annual Book of
ASTM Standards volume information, refer to the standard’s Document Summary
page on the ASTM website.
3
Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),
445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
1

moisture and vibration, will cause failures after the material

has been weakened by thermal degradation.

5.2 Electrical insulation is effective in electrical equipment

only as long as it retains its physical and electrical integrity.

The following are potential indicators of thermal degradation:

weight change, porosity, crazing, and generally a reduction in

ﬂexibility. Thermal degradation is usually accompanied by an

ultimate reduction in dielectric breakdown.

5.3 This test method is useful in determining the thermal

endurance of coating powders applied over a steel substrate

material.

6. Apparatus

6.1 Dielectric Breakdown Test Set—The set shall meet the

requirements of Test Method D149.

6.2 Ovens—Ovens shall meet the requirements of Speciﬁ-

cation D5423, Type I.

6.3 Electrically Conductive Solution:

6.3.1 An appropriate container shall be selected for the

electrically conductive solution.

6.3.2 Prepare a solution having a conductivity of at least

2.5 mS (millisiemens).

NOTE 1—A solution comprised of tap water and a solute such as NaCl

or NH

Cl has been found to be acceptable. Since the water solution is used

to detect (not cause) material decomposition/breakdown, the solution is

acceptable for use as long as it meets the minimum conductivity

requirements. It is recommended to change the solution when it becomes

difficult to observe breakdown due to cloudiness or other contamination.

6.3.3 During testing, the conductive solution is at ground

potential. The ground connection, using an immersed

electrode, is made using Nichrome, stainless steel, or other

non-corrosive metal.

6.3.4 Fit the container with a cover to prevent evaporation

of the solution when not in use.

7. Hazards

7.1 Warning—Lethal voltages are a potential hazard during

the performance of this test. It is essential that the test

apparatus, and all associated equipment electrically connected

to it, be properly designed and installed for safe operation.

Solidly ground all electrically conductive parts which are

possible for a person to contact during the test. Provide means

for use at the completion of any test to ground any parts which

were at high voltage during the test, or have the potential for

acquiring an induced charge during the test, or retaining a

charge even after disconnection of the voltage source. Thor-

oughly instruct all operators as to the correct procedures for

performing tests safely. When making high voltage tests,

particularly in compressed gas or in oil, it is possible for the

energy released at breakdown to be sufficient to result in ﬁre,

explosion, or rupture of the test chamber. Design test

equipment, test chambers, and test specimens so as to minimize

the possibility of such occurrences and to eliminate the

possibility of personal injury. If the potential for ﬁre exists,

have ﬁre suppression equipment available.

8. Test Specimens

8.1 The substrate material to be used for evaluating integral

bus-bar insulation systems shall be steel. It is preferred that the

conﬁguration of the substrate material be representative of the

end application. One conﬁguration that has been found to be

useful is shown in Fig. 1. Alternative conﬁgurations are

acceptable if agreed to by all interested parties.

8.2 The substrate shall be coated with the powder and cured

using the manufacturer’s standard process. One end of the

specimens shall be left uncoated for making an electrical

connection during the dielectric strength tests.

9. Number of Test Specimens

9.1 A set of specimens for thermal aging shall consist of at

least ten specimens. Prepare one set for each aging temperature

chosen.

9.2 The initial value (unaged) set shall consist of at least

twenty specimens.

9.3 The minimum number of test specimens is 50. It is

recommended to prepare extra specimens for situations such as

FIG. 1 Example Specimen Dimensions

D7895/D7895M − 19 (2025)

the need to add additional aging temperatures, or to have

replacement specimens available for any specimens that are

found during the screening test to be unsuitable for use in

thermal aging.

10. Calibration and Standardization

10.1 Expose the test material to at least three aging tem-

peratures. The preferred number of aging temperatures is four.

10.2 Minimum thermal life target values for the high and

low temperatures shall be selected based on application.

10.3 Aging temperatures shall differ by at least 10 °C.

NOTE 2—Experience has shown that the suggested target thermal life

values listed in Table 1 are generally satisfactory.

11. Selection of Aging Cycles

11.1 To provide approximately equal exposures to the other

conditionings, and to more accurately determine the property

endpoint, the heat aging time per cycle shall be shorter for the

higher aging temperatures and longer for the lower aging

temperatures.

11.2 Cycle times shall be selected such that each set

undergoes an adequate (but not excessive) number of cycles

before completion. In order to obtain an appropriate number of

cycles, the following adjustments to the cycle time are recom-

mended:

11.2.1 If no specimens in a set fail by the end of the 4

cycle, double the heat aging period of the test cycle.

11.2.2 If three or more specimens in a set fail by the end of

the 4

cycle, halve the heat aging period of the test cycle.

11.2.3 Use observations in the highest temperature set to

select appropriate adjustments to the other temperature sets.

NOTE 3—Experience has shown that the suggested cycle times in Table

1are generally satisfactory.

12. Initial Value Test

12.1 To determine an initial dielectric strength level, at least

twenty specimens shall be selected at random from the sample

and subjected to a voltage breakdown test.

12.2 Connect one electrode of the tester to the uncoated end

of the specimen. Suspend the coated end of the specimen in the

electrically conductive solution described in 6.3.2 (see Fig. 2).

The total surface area to be tested shall be sufficient to be

representative of the intended application.

12.3 Apply voltage uniformly to the test electrode in accor-

dance with the guidelines of the Short-Time Test described in

12.2.1 of Test Method D149, unless another rate is speciﬁed,

until breakdown occurs.

12.4 Make one measurement on each specimen and com-

pute the average dielectric breakdown voltage for the set.

Record this as the initial value.

13. Screening Test

13.1 Prior to thermal aging, all specimens shall be subjected

to a screening test in order to remove defective units. Any

specimen that cannot pass the screening test shall be discarded

and a replacement specimen selected for thermal aging.

13.2 Select a screening test voltage level that is a percentage

of the average initial value.

13.3 Select a screening test period of time that is expected to

cause failure in weak specimens without causing damage to the

remaining specimens.

NOTE 4—Experience has shown that a screening test voltage level of

75 % of the initial value for a period of 10 s is generally satisfactory.

13.4 Suspend each specimen in the electrically conductive

solution in the same manner as described for the initial value

test. Apply voltage uniformly to the test electrode in accor-

dance with the guidelines of the Short-Time Test described in

12.2.1 of Test Method D149, unless another rate is speciﬁed,

until the screening voltage level is achieved. Maintain the

voltage for the screening test period before removing the

voltage from the specimen.

13.5 Discard any specimen that breaks down. Specimens

that do not break down during the screening test are acceptable

for use in the thermal aging.

14. Procedure

14.1 Thermal Aging of Specimens—Tag four sets of speci-

mens by any reliably permanent means and expose the sets in

the oven at each of the selected temperatures. Position the sets

so that free movement of air exists across the entire specimen.

14.2 Stress Cycling:

14.2.1 Following the completion of each thermal exposure,

all specimens in the set shall be removed from the oven and

allowed to cool to 23 °C 62 °C.

14.2.2 All specimens shall then be subjected to a cold

exposure and allowed to reach equilibrium with the cold

environment.

14.2.2.1 If the coating resin is intended for outdoor

applications, the cold exposure temperature shall be minus

20.0 °C 62.0 °C [minus 4.0 °F 63.6 °F].

14.2.2.2 If the coating resin is intended for indoor

applications, the cold exposure temperature shall be 0.0 °C 6

2.0 °C [32.0 °F 63.6 °F].

14.2.3 Following the cold exposure, all specimens shall be

allowed to return to 23 °C 62 °C.

14.2.4 All specimens shall then be mounted on a shake table

and operated for a period of 10 000 cycles with a 60 Hz

oscillating motion and an acceleration of 7 G’s.

14.2.4.1 The specimens shall be mounted such that the

motion occurs at right angles to the largest ﬂat surface of the

specimen and parallel to the smallest ﬂat surface of the

specimen (see Fig. 3).

14.2.5 Following the vibration exposure, all specimens shall

be placed into a humidity exposure for a minimum of 24 h at

TABLE 1 Suggested Cycle Times and Target Lives

Temperature Set Cycle Time Target Life

High Temperature 48–72 h 400–700 h

Middle High Temperature 168 h 1000–1500 h

Middle Low Temperature 336 h 2000–3000 h

Low Temperature 504 h 5000+ h

D7895/D7895M − 19 (2025)

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

亲，本站95%以上的标准规范都面向会员免费，办理VIP会员下载更省钱，平均每篇不到2元

立即下载 VIP免费下载

标签： #标准试验 #试验方法 #标准试验方法

摘要：

本页面详细介绍ASTM D7895 - D 7895M - 19 (2025)标准试验方法，该标准用于评估粉末涂覆绝缘系统所用涂层粉末的热耐久性。通过规范化的热老化测试程序，帮助制造商、工程师和质量控制人员确定粉末涂层在高温环境下的性能保持能力，从而确保绝缘系统的长期可靠性与安全性。内容涵盖测试原理、试样制备、加热循环条件、性能评定指标以及结果报告要求，适用于电力设备、电机绕组、变压器及电子元器件等领域的粉末涂覆绝缘材料选型与质量验证。本标准的发布替代或更新了早期版本，并提供了公制与非公制单位（

展开>> 收起<<

ASTM D7895 - D 7895M - 19 (2025) 粉末涂覆绝缘系统用涂层粉末热耐久性的标准试验方法.pdf

共6页,预览3页

还剩页未读，继续阅读

声明：本文档系会员上传，若文档所含内容侵犯了您的版权或隐私，请立即通知，我们立即给予侵权申诉删除！

ASTM D7895 - D 7895M - 19 (2025) 粉末涂覆绝缘系统用涂层粉末热耐久性的标准试验方法

相关推荐

开通VIP享超值会员特权

相关内容

热门标签

举报选择: